geol599 strain localization...
TRANSCRIPT
GEOL599 Strain localizationIntroduction
Localization mechanisms
● Rarefied zones in granular media facilitate dilatation
● Brittle material hosts cracks and voids which lead to stress concentrations
● Stress dependent grain size and grain size dependent viscosity
● Viscous heating and temperature dependent viscosity
How do these processes interact in the brittle-ductile transition to form
plate boundaries?
Minor questions...
● What is the constitutive law for faults? ● How do fault systems (and seismic hazard
evolve)? ● How are plate boundaries formed and
maintained?● What is the role of transform faults for plate
tectonics? ● What controls the efficiency of mantle
convection?● What makes Earth have plate tectonics, while
other planets ended up empty handed?
Ramsay (1970)
Brittle shear zone
Byerlee (1978)
Resistance to sliding on existing planes
Rutter et al. (2001)
Comparison of Byerlee with in situ stress
Aydin (1978)
Deformation bands in sand stone
2 mm
Aydin and Johnson (1978)
Deformation zones Slip surfaces
Brittle fault system evolution
Aydin and Johnson (1978)
Brittle fault system evolution
Ben-Zion and Sammis (2003)
Ben-Zion and Sammis (2003)
A fault constitutive law that captures all spatio-temporal scales of strain
release does not exist
● But there are heuristic frictional descriptions● And there are damage theories
Marone (1998)
Rate and state friction
One state variable limit cycle
Becker (1999)
Two state variables period doubling
Becker (1999)
Becker (1999)
Scholz (2003)
Stability
Scholz (2003)
Ramsay (1970)
Ramsay (1970)
Ramsay (1970)
Rutter et al. (2001)
~ 50 kmRutter et al. (2001)
Kohlstedt et al. (1995)
Goetze/Peierls creep
Dislocation creep Diffusion creep
Byerlee's law
Brittle - plastic
Ductile
Kohlstedt et al. (1995)
Kohlstedt et al. (1995)
Kohlstedt et al. (1995)
Most of the strength in oceanic lithosphere resides in the poorly
understood transition region between brittle and ductile domain
First principles damage theories
● Elastic● Viscous
Ashby and Sammis (1990)
Ashby and Sammis (1990)
Lyachovsky et al. (1997)
or
Lyachovsky et al. (2001)
Bercovici et al. (2001); Landuyt et al. (2008)
Void-volatile, surface energy theory in the porosity(void)-fineness limit
Bercovici et al. (2001)
Landuyt et al. (2008)
So how does plate tectonics work?
And can we use large scale dynamics as a constraint for
rheology?
Kreemer et al. (2001)
HS3
poloidal
toroidal
RVV flow model
Becker (2006)
new hotspotref. frame
(HS3)
geodesymodel
(GSRM)
viscosity depth
dependent
viscositytemp.
dependent
dry olivine
creep law
tectonicmodels
geodynamicmodels
Becker (2006)
Bercovici (1995)
Which rheology creates the weak zones?
Bercovici (1995)
Bercovici (1995)
Richards et al. (2002)
Convection models
Tackley (2000)
Increase
in yield
stress
Foley & Becker (2009)
Tackley (2000)
ar = f(d
ss)= f(B -p)
The role of memory
Additional stuff
Constant strain Constant force Constant effectiveforce
Porth (2002)